Voltage supply amplitude modulation driving outlier microleds

ABSTRACT

A micro light emitting diode (LED) die can include a matrix of micro LEDs with a variety of forward voltages. A method of reducing a number of undriven or under driven uLEDs can include providing, by a power supply, an alternating current voltage (VLED) with a minimum voltage (VMIN) and a maximum voltage (VMAX), VMIN being sufficient to drive a plurality of micro light emitting diodes (uLEDs) of a uLED die using a plurality of uLED drivers, identifying, by a controller coupled to the uLED drivers, a uLED of the plurality of uLEDs with a forward voltage (Vf) greater than VMIN, and altering, by the controller, a time of a rising edge of a pulse width modulation (PWM)-on time of the uLED such that Vf of the uLED is less than VLED for the PWM-on time.

TECHNICAL FIELD

The present disclosure relates to a light-emitting apparatus and alight-emitting apparatus control system configured to reduce oreliminate dark aberrations experienced with an abnormally high forwardvoltage.

BACKGROUND

In some applications, such as home or commercial lighting, userexperience of the lighting is very important. Automotive lighting isanother application in which user experience is very important. If aforward voltage of a light emitting diode (LED) is above the supplyvoltage, the LED will likely not operate as expected. Such LEDs canappear as black or darker spots among lit LEDs.

BRIEF DESCRIPTION OF THE DRAWINGS

The figures show various views of an apparatus, system, or method,including a control system that can alter light emerging from one ormore light emitting diodes (LEDs), in accordance with some embodiments.The terms “front,” “rear,” “top,” “side,” and other directional termsare used merely for convenience in describing the apparatuses andsystems and other elements and should not be construed as limiting inany way.

FIG. 1 illustrates, by way of example, a logical block diagram of anembodiment of a system for driving a die including a matrix of microLEDs (uLEDs).

FIG. 2 illustrates, by way of example, a perspective view of anembodiment of a uLED die that includes undriven and/or underdrivenuLEDs.

FIG. 3 illustrates, by way of example, a graph of driver circuitelectrical efficiency versus uLED forward voltage (V_(f)).

FIG. 4 illustrates, by way of example, a conceptual block diagram of anembodiment of a package including a matrix of uLEDs and correspondingdriver circuitry.

FIG. 5 illustrates, by way of example, a circuit diagram of anembodiment of a uLED pixel (uLED driver circuitry and a correspondinguLED).

FIG. 6 illustrates, by way of example, a graph of forward voltage (Vf)of uLEDs vs duty cycle for a typical matrix of uLEDs.

FIG. 7 illustrates, by way of example, a logical circuit diagram of anembodiment of a system that considers outlier pixel Vf to drive thematrix of uLEDs.

FIG. 8 illustrates, by way of example, a graph of a modulated voltagesupply (V_(LED)) and a corresponding uLED response.

FIG. 9 illustrates, by way of example, a graph of electrical parametersversus time of an embodiment.

FIG. 10 illustrates, by way of example, a graph of electrical parametersversus time of an embodiment of an outlier uLED (outlier defined asV_(f)>V_(LED) for at least a portion of time).

FIG. 11 illustrates, by way of example, a graph of electrical parametersversus time of an embodiment of an outlier uLED.

FIG. 12 illustrates, by way of example, a graph of electrical parametersversus time of an embodiment of an outlier uLED.

FIG. 13 illustrates, by way of example, a graph of electrical parametersversus time of an embodiment of an outlier uLED before and afteralteration of the uLED on time to ensure that the uLED V_(f)<V_(LED)during a PWM-on period of the uLED.

FIG. 14 illustrates, by way of example, a graph of electrical parametersversus time of an embodiment of an outlier uLED before and afteralteration of the uLED on time.

FIG. 15 illustrates, by way of example, a graph of electrical parametersversus time of an embodiment of an outlier uLED before and afteralteration of the uLED on time.

FIG. 16 illustrates, by way of example, a block diagram of an embodimentof a system for adjusting uLED PWM-on period.

FIG. 17 illustrates, by way of example, a diagram of an embodiment of amethod for driving a uLED matrix die.

FIG. 18 illustrates in more detail an embodiment of a chip-levelimplementation of a system supporting functionality, such as discussedwith respect to, for example, FIGS. 6-17.

FIG. 19 illustrates, by way of example, a logical block diagram of asystem that includes circuitry that can be included in a uLED package.

FIG. 20 illustrates, by way of example, a block diagram of an embodimentof a machine (e.g., a computer system) to implement one or moreembodiments.

DETAILED DESCRIPTION

Compact, pixelated LEDs, such as in an array of micro LEDs (sometimespresented as “uLED”) on a uLED die, can include a large monolithic area.The uLED array can be used for automotive lighting, such as headlights,taillights, parking lights, fog lamps, direction lights, or the like.Such applications are merely examples and many other applications ofuLED arrays are possible.

The uLED array can include a die of uLEDs hybridized with driverelectronics for the control of individual pixel brightness. The driverelectronics can be manufactured using, for example, complementary metaloxide semiconductor (CMOS) materials or processes or other semiconductormanufacturing processes.

In some embodiments, the driver electronics can implement a lineardriving scheme. The linear driving schemes are practical solutions forsuch control electronics, particularly for large uLED arrayconfigurations. However, special care is demanded in a linear drivingscheme to control the voltage supply to the driver electronics, such asto provide both stable uLED current supply and acceptable heat losses.To guarantee that all pixel drivers are operated above their compliancevoltage, the voltage supply to the driver electronics is generally setabove the highest forward voltage (V_(f)) of the uLEDs in the array.

An advantage of monolithic uLED chips is that they favor a narrowdispersion of forward voltages (V_(f)) among the uLED population (e.g.,standard deviations <100 milli-Volts). This forward voltage (V_(f))homogeneity reduces heat loss, such as by reducing a voltage differencebetween a voltage supplied and the forward voltage (V_(f)) of the uLEDs.Unfortunately, there still exists a small but relevant group of outlieruLEDs whose forward voltage (V_(f)) is excessively high (e.g., greaterthan 20%, 25%, a greater or lesser percentage, or a percentagetherebetween higher than the average forward voltage (V_(f)) of theuLEDs).

One solution to providing sufficient supply voltage includes providing asupply voltage that is greater than (or equal to) a highest V_(f) forall of the uLEDs on the die, including the outliers. Using thissolution, all uLEDs, including the outliers, will be properly driven.However, heat losses will increase (in some practical cases, toprohibitive levels) as the voltage drop across the driver electronicswill, on average, increase.

Another solution includes no consideration for outlier uLEDs. Suchskipping of outliers allows the supply voltage to remain low, therebybenefiting from the narrow forward voltage (V_(f)) dispersion among theuLEDs. In this solution, heat losses will be reduced compared to thesolution that increases the voltage supply voltage to account for one ormore of the V_(f) of outliers. However, using such a solution, it islikely that some outlier uLEDs will be undriven and/or underdriven. Suchundriven and/or under driven uLEDs can appear as dark spots on the uLEDarray. A bigger population of outliers can be prohibitive in someapplications, especially if the undriven or under driven uLEDs remainvisible.

Embodiments can include a (e.g., simple) driving scheme to providevoltage compliance to outlier uLED drivers so that the correspondinguLEDs can light up with minor impact on heat losses. Advantages providedby embodiments can address one or more of the following challenges ofpixelated matrix LEDs driven with linear driver schemes: (1) providing acost-effective driving scheme of matrix uLEDs; (2) overcoming driverefficiency limitations; (3) overcoming voltage compliance limitations;or (4) addressing forward voltage dispersion across population of pixelswhere outliers compromise either voltage compliance or driverefficiency.

FIG. 1 illustrates, by way of example, a diagram of an embodiment of auLED control system 100. The system 100 as illustrated includes avoltage supply 102 that provides power distributed by a plurality of LEDdrivers to a matrix of uLEDs 104. The voltage supply 102 provides aconstant direct current (DC) voltage V_(LED) 106 and a constantreference voltage V_(GND) 108. The voltage supply 102 can fix thevoltage supply to the DC level of V_(LED) 106. This voltage does notdynamically change with a load line response (a load of the array ofuLED 104). Thus, V_(LED) 106 does not change dynamically change during apulse width modulation (PWM)-on period of the current driver signals.

As previously discussed, if V_(LED) 106 is set to account for theoutlier pixels of the array of uLEDs 104, the heat losses in the driversof the uLEDs will be high (even prohibitively high). Conversely, if theV_(LED) 106 is set without consideration of the V_(f) of the outlieruLEDs, the outlier uLEDs can remain undriven or under driven. Suchundriven or under driven LEDs can appear as dark spots in the matrix ofuLEDs 104.

FIG. 2 illustrates, by way of example, a diagram of an embodiment of anarray of uLEDs 200 driven without consideration of V_(f) of the outlieruLEDs. As can be seen, some uLEDs remain undriven or under driven,resulting in black or darker spots 220 in the array of uLEDs 200.

FIG. 3 illustrates, by way of example, a diagram of an embodiment of agraph of efficiency versus number of outlier uLEDs (as a % of all uLEDsin the array of uLEDs 200). As can be seen, as the percentage of pixelsthat are considered outliers increases, the driver circuit electricalefficiency decreases. A goal can be to keep the electrical efficiencygreater than, for example, 85%, 80%, a greater of lesser percentage orsome percentage therebetween. Electrical efficiency is defined as poweroutput divided by the power provided. For example, if the outlier V_(f)increases by 20% over the population of LEDs in the matrix of uLEDs 104,the driver efficiency drops from 86% (reference efficiency consideringno outliers) down to 72%.

FIG. 4 illustrates, by way of example, a logical block diagram of anembodiment of a system 400 including an electrical backplaneelectrically coupled to the matrix of uLEDs 104. The electricalbackplane includes uLED drivers 444 and power provisioning circuitry.Further details of a linear driver version of the uLED drivers 444 areprovided regarding FIG. 5. The power provisioning circuitry includesV_(LED) 106 and the reference voltage V_(GND) 108 from the power supply.The V_(LED) 106 is provided to a power plane 442. The V_(GND) 108 isprovided to a ground plane 440. The uLED drivers 444 are powered usingthe V_(LED) 106 from the power plane 442. The uLED drivers 444 control,via an electrical interconnect 446 individual or groups of uLEDs in thematrix of uLEDS 104. The uLED drivers 444 can control whether the uLEDis on, off, a duty cycle, or other power control of the uLEDs 104.

The matrix of uLEDs 104 are electrically coupled to the uLED drivers 444through the electrical interconnects 446. The matrix of uLEDs 104 areelectrically coupled to the ground plane 440 through other electricalinterconnects 448. A dielectric 450 electrically and physicallyseparates the uLED drivers 444 from the ground plane 440. That is, thedielectric 450 is situated (e.g., directly) between the uLED drivers 444and the ground plane 440 and (e.g., directly) between the ground plane440 and the power plane 442.

FIG. 5 illustrates, by way of example, a logical circuit diagram of anembodiment of a system 500 that includes the uLED driver 444 and a uLED550 of the matrix of uLEDs 104. The uLED driver 444 controls anelectrical signal 554 on the electrical interconnect 446. The uLEDdriver 444, by controlling the electrical signal 554, can inhibit orallow current to flow to the uLED 550. Using this control, the uLEDdriver 444 can control whether and when the individual or group of uLEDs550 is on and the duty cycle of the uLEDs.

To overcome the limitations of other uLED driving schemes and toincrease electrical efficiency of a matrix of uLEDs 104, some improveddriving schemes are provided. Embodiments consider uLED dies withindividually addressable pixels. The uLED dies include uLED drivers 444that include linear driver architectures operating in PWM mode. Thecontrol scheme(s) can help minimize or reduce the total root mean square(RMS) and harmonic current driven by the voltage supply 102, by at leastin part, the phases of pulse width modulation (PWM) control signals ofthe uLEDs being randomized.

Embodiments can include a voltage supply 102, the output voltage ofwhich can be dynamically modulated and controlled by a load (e.g., acontroller 1660 of the load (see FIG. 16)) with a sufficient bandwidthresponse Embodiments can include a control scheme wherein outlier pixelscan be identified (e.g., by means of a sensing voltage, and classifiedas such (see FIG. 16)), before or during runtime of the matrix of uLEDs104. The controller 1660 can cause the voltage from the voltage supply102 to increase to a specified voltage value during every cycle or everyseveral cycles of the PWM signal of the drivers. The higher voltage canbe specified as a function of a distribution of the forward voltages(V_(f)) of the outlier pixels.

Embodiments can include a control scheme that repeatedly (e.g.,periodically, such as at predefined intervals) increases the voltagesupply to a specified voltage value during every cycle or every severalcycles of the PWM signal of the drivers. Said higher set voltage can bespecified as a function of the forward voltage (V_(f)) of the outlierpixels. A forward voltage (V_(f)) of an LED is the voltage drop acrossthe LED while the LED is illuminating.

Embodiments can include a control scheme wherein the random PWM phasecontrol of the identified outlier pixels can be synchronized with anincrease of the power supply voltage. Embodiments can include a controlscheme to synchronize the rise of the voltage provided by the powersupply with the PWM signals of the outlier pixels such that theircompliance voltage can be satisfied at least during a period establishedby the increase in supply voltage. Embodiments can provide a controlscheme that includes a modifiable set current of outlier pixels.

Temperature gradients are an important consideration in large areamatrix arrays. A typical duty cycle map renders a power densitydistribution and a temperature distribution such that the forwardvoltage variation changes significantly between the regions of highpower density and the regions of low power density, resulting in a V_(f)spread >150 mV. Adding the V_(f) dispersion of the manufacturingprocess, the V_(f) spread may be higher than 400 mV. Plotting therequired voltage compliance as a function of duty cycle of such pixelconfiguration reveals that V_(f) decreases with the increase of dutycycle.

FIG. 6 illustrates, by way of example, a graph 600 of forward voltage(V_(f)) of uLEDs versus duty cycle for a typical matrix of uLEDs 104(see, e.g., FIG. 1). As can be seen, the forward voltage (V_(f))generally decreases with duty cycle. A reason for this trend is that theforward voltage (V_(f)) drops with an increase in temperature and thehigher the duty cycle the hotter the uLED (in general). Therelationships between V_(f), temperature, and duty cycle can beexploited to apply a supply voltage to more optimally drive uLEDs withdifferent duty cycles. These relationships include, for example: uLEDsoperating with high duty cycle have a higher temperature hotter and sotheir V_(f) tends to be lower and uLEDs operating with low duty cyclerun cooler so their V_(f) tends to be higher.

Some example load-lines 660, 662, 664 are depicted in FIG. 6. Note thatthe steeper the slope of the load line gets (the slope of the load-line660 is greater than the slope of the load line 662, etc.), the higherthe number of uLEDs that will not fulfil a voltage compliance condition(e.g., V_(LED)>V_(f), note that load-lines 660, 662, 664 representV_(LED)), and hence these pixels may be driven below their set currentlevels. Embodiments discussed herein strike a balance between the numberof outlier uLEDs that are not driven by V_(LED) and the temperatureconcerns of having V_(LED) too high for too long.

FIG. 7 illustrates, by way of example, a logical circuit diagram of anembodiment of a system 700 that considers outlier pixel V_(f) to drivethe matrix of uLEDs 104. The system 700 is similar to the system 100 ofFIG. 1, with the system 700 including circuitry to provide a controlcommand 760 to the voltage supply 102. The control command 760 indicatesthat the voltage supply 102 is to supply a higher voltage in a nextvoltage supply period. The control command 760 can be issued by acontroller 1660 (see FIG. 9) coupled to the uLED drivers 444. Thevoltage (V_(LED)) supplied by the voltage supply 102 includessufficiently dynamic control bandwidth for establishing a modulatedsignal of the same or similar frequency as that of a PWM currentproduced by the driver 444.

FIG. 8 illustrates, by way of example, a graph 800 of a modulatedvoltage supply (e.g., V_(LED) 106 of FIG. 1) and a corresponding uLEDresponse. The uLED response is represented by a duty cycle on period886. The modulated supply voltage (V_(LED) 106) in FIG. 8 oscillatesbetween voltage levels (V_(MIN) 884 and V_(MAX) 880) above thecompliance voltage (forward voltage (V_(f)) 884) of a uLED. Thus, suchuLED receives a pulse width modulation (PWM) power signal with randomphase shifted on period 886 that can be triggered anywhere within thecycle period by the driver 444. Arrow 888 indicates the random phaseshift.

Examples of V_(MIN) 884 and V_(MAX) 880 are dependent on materials ofthe uLEDs. For InGaN blue, V_(MIN) 884 can be about 2.5V and V_(MAX) 880can be about 5V. For AlInGaP V_(MIN) 884 can be about 1.5V and V_(MAX)880 can be about 4V. Other materials can have different V_(MIN) 884 andV_(MAX) 880.

A different situation occurs when the forward voltage of a uLED is aboveV_(MIN) 884. Such uLEDs are considered outliers. For such uLEDs, acontroller 1660 (described below with reference to FIG. 16) can monitoran on-state of the uLED and help ensure that the on time of the uLEDdoes not fall within a time interval in which V_(f)>V_(L)ED. Thecontroller 1660 can alter timing of signals to driver 444, such as tohelp ensure that the uLED has sufficient voltage for operation and getsas much on time as is allowed until V_(LED)<V_(f) again. FIGS. 9-15discuss a few scenarios handled by embodiments in which V_(f)>V_(LED)for at least a portion of a modulation period of V_(LED) 106. Amodulation period is a time between consecutive times at whichV_(LED)=V_(MAX) or at which V_(LED)=V_(MIN).

When there is a choice to shift the phase to either before or after aportion of the period where V_(LED)>V_(f) (labelled as the disabledphase in FIGS. 9-13), the phases can be shifted to before, after, or acombination thereof of the disabled phase. In splitting the on-phase ofthe uLED to before and after the disabled period can allow the correctedphases to be more uniformly distributed over one PWM period. Thisuniform distribution provides for lower root mean square (RMS) andharmonic currents. Such a change that splits the period to before andafter the disabled phase are provided in some of the FIGS.

FIG. 9 illustrates, by way of example, a graph 900 of electricalparameters versus time of an embodiment. The electrical parametersincludes V_(LED) 106, PWM-on time 990 of a uLED before correction, andPWM-on time 992 of the uLED after correction. A disabled phase 994 foruLEDS includes a time period for which the forward voltage of the uLEDis greater than a supply voltage V_(LED) (V_(f)>V_(LED)).

The controller 1660 can have access to data indicating the V_(f) 882 ofthe uLED, V_(MAX) 880, V_(MIN) 884, and frequency of V_(LED) 106provided by the voltage supply 102, and duty cycle of the uLED. Thecontroller 1660 can use this data to determine when to send a command tothe driver 444 to drive the uLED. The command can cause the driver 444to turn the uLED on. The command can be issued so that the PWM-on time990 of the uLED does not overlap with a time period for which theforward voltage 882 of the uLED is greater than the supply voltageV_(LED) (V_(f)>V_(LED)) (the disabled phase 994). The PWM-on time 992shows such an adjusted PWM-on time that does not overlap with thedisabled phase 994. The adjustment of the PWM on-time is indicated byarrows 996 and 998.

FIG. 10 illustrates, by way of example, a graph 1000 of electricalparameters versus time of an embodiment of an outlier uLED (outlierdefined as V_(f)>V_(LED) for at least a portion of time). The uLED ofFIG. 10 includes a duty cycle 1010 that corresponds to a duration thatis less than an amount of time that V_(f)>V_(LED) in an incline ordecline of the V_(LED) 106 over a single cycle (time betweenV_(LED)=V_(MAX) or V_(LED)=V_(MIN)). In such an instance, the controller1660 can issue a command that causes the uLED driver 444 to drive theuLED so that the PWM-on period 1012 after correction ends at about thetime V_(f)=V_(LED) or begins at about the time V_(f)=V_(LED). In theexample of FIG. 11, described in more detail below, the controller 1660has adjusted the PWM-on period 1110 to end at about the timeV_(f)=V_(LED). An amount of correction is indicated by arrows 1014, 1016of equal magnitude. The controller 1660 can determine a time at whichV_(f)>V_(LED) (the disabled phase 994) and adjust the on time to stillsatisfy the duty cycle of the uLED.

FIG. 11 illustrates, by way of example, a graph 1100 of electricalparameters versus time of an embodiment of an outlier uLED. The uLED ofFIG. 11 includes a PWM-on period 1110 (corresponding to a duty cycle)that corresponds to a duration that is less than an amount of time thatV_(f)>V_(LED) in an incline (time period over which a slop of V_(LED) vstime is positive) or decline (time period over which the slope ofV_(LED) vs time is negative) of the V_(LED) 106 over a single cycle(time between V_(LED)=V_(MAX) or V_(LED)=V_(MIN)). In such an instance,the controller 1660 can issue a command that causes the uLED driver 444to drive the uLED so that the PWM-on period 1112 after correction endsat about the time V_(f)=V_(L)ED or begins at about the timeV_(f)=V_(LED). In the example of FIG. 11, the controller 1660 hasadjusted the PWM-on period 1110 to begin at about the timeV_(f)=V_(LED). An amount of correction is indicated by arrows 1114, 1116of equal magnitude. The controller 1660 can determine a time at whichV_(f)>V_(LED) (the disabled phase 994) and adjust the on time to stillsatisfy the duty cycle of the uLED.

FIG. 12 illustrates, by way of example, a graph 1200 of electricalparameters versus time of an embodiment of an outlier uLED. In theexample of FIG. 12, the uLED can be scheduled to power on and off (anentirety of the PWM-on period of the uLED) falls within the disabledphase 994. In such an instance, the controller 1660 can choose to movethe PWM-on period to before or after the V_(LED)<V_(f). In the exampleof FIG. 12, the controller 1660 moved the PWM-on period 1210 of the uLEDto before a time V_(LED)<V_(f) and such that the entirety of the PWM-onperiod 1210 occurs while V_(LED)>V_(f). To do this, the controller 1660can, for example, determine a difference between an expected fallingedge of the PWM-on period 1210 and a time before the PWM-on period 1210that V_(LED) 106=V_(f) 882 (indicated by dashed line 1218). In anotherexample, the controller 1660 can determine a difference between anexpected rising edge of the PWM-on period 1210 and a time after thePWM-on period 1210 that V_(LED) 106=V_(f) 882 (indicated by dashed line1220).

The difference between the falling edge of the PWM-on period 1210 andthe time before the PWM-on period 1210 at which V_(LED) 106=V_(f) 882 isindicated by arrow 1214. This difference can be used to adjust the timeat which the rising edge of the PWM-on period 1210 begins (indicated byarrow 1216). A corrected PWM-on period 1212, that accounts for theadjustment indicated by the arrow 1216, moves the PWM-on period 1212 ofthe uLED to be within a time period at which V_(f)<V_(LED) (outside thedisabled phase 994).

FIG. 13 illustrates, by way of example, a graph 1300 of electricalparameters versus time of an embodiment of an outlier uLED before andafter alteration of the uLED on time to ensure that the uLEDV_(f)<V_(LED) during a PWM-on period of the uLED. In the example of FIG.13, a frequency of V_(LED) 106 is such that V_(LED) cycles multipletimes (equals either VMAX 880 or VMIN 884 multiple times) between PWM-onperiods 1330, 1332 of the uLED. In such examples, time correction isonly performed when the PWM-on period 1330, 1332 overlaps with thedisabled phase 994.

In FIG. 13, the time between occurrences of V_(LED) 106=V_(MAX) is lessthan the time between PWM-on periods 1330, 1332. If the time betweenconsecutive PWM-on periods 1330, 1332 (e.g., between rising edges ofconsecutive PWM-on periods 1330, 1332) is not an integer multiple of thetime between occurrences of V_(LED) 106=V_(MAX) 880, the adjustment ofthe PWM-on period 1330 (indicated by arrows 1338, 1340) can change ineach cycle. If the time between consecutive PWM-on periods 1330, 1332 isan integer multiple of the time between occurrences of V_(LED)106=V_(MAX) 880, the adjustment (indicated by arrows 1338, 1340) of thePWM-on period 1330 rising edge time can remain the same. The adjustmentsmade to the PWM-on periods 1330, 1332 are illustrated as PWM-on periods1334, 1336, respectively, and the adjustments made are indicated byarrows 1342, 1344 of same magnitude as 1338, 1340, respectively.

FIG. 14 illustrates, by way of example, a graph 1400 of electricalparameters versus time of an embodiment of an outlier uLED before andafter alteration of the uLED on time. In the example of FIG. 14, thePWM-on time 1440 of the uLED is greater than an amount of time thatV_(LED) 106 is greater than V_(f) 882 of the uLED. Even after PWM-ontime adjustment, indicated by arrows 1444 and 1446, the amount of timeV_(LED)>V_(f) is less than the PWM-on time. In such situations it mightbe possible to adjust a parameter (e.g., drive current, PWM on-time, orother parameter) of the uLED or one or more neighboring uLEDs tocompensate for the reduced duty cycle of the uLED. One potentialsolution to this issue is to do nothing, such as if the amount of PWM-ontime that is lost (indicated by arrow 1448) does not visibly alter theappearance of the image. This can be acceptable depending on a reductionin uLED intensity provided by the reduction in PWM-on time as well asthe number of outlier uLEDs.

Another solution to the issue of losing PWM-on time includes increasingthe V_(MIN) 884. This solution increases the heat produced and reducesthe electrical efficiency of the matrix of uLEDs 104 to increase theamount of time that V_(LED) 106 is greater than V_(f) 882. The time whenV_(f) 882 >V_(LED) 106 will be reduced, allowing to increase the on-timeof the pixel.

Yet another solution to the issue of losing PWM-on time includesreducing the duty cycle and increasing a peak current of the uLED driver444 locally (only for the uLEDs with V_(f) 882 >V_(LED) 106 and withduty cycle corresponding to PWM-on time greater than an amount of timethat V_(LED) 106>V_(f) 882. This solution can keep the same targetaverage current, but the increase of the peak intensity will increaseV_(f) as well as reduce efficiency due to the intrinsic uLED voltagedrop.

FIG. 15 illustrates, by way of example, a graph 1500 of electricalparameters versus time of an embodiment of an outlier uLED before andafter alteration of the uLED on time. In FIG. 15, V_(MAX) 880 andV_(MIN) 884 have been increased relative to that of FIG. 14. This allowsthe disabled phase 994 of the uLED to be reduced such that the PWM-ontime 1440 can be accommodated without having overlap between thedisabled phase 994 and the PWM-on time 1442 (after compensation).

FIG. 16 illustrates, by way of example, a block diagram of an embodimentof a system 1600 for adjusting uLED 550 PWM-on time. The system 1600includes the controller 1660 coupled to a memory 1662. The controller1660 is further coupled to control uLED drivers 444, which driverespective uLEDs 550. The memory 1662, as illustrated, includes (foreach uLED 550) a uLED identification (e.g., a row and column of the uLED550 in the matrix of uLEDs 104 or other unique identification of theuLED 550). The memory 1662 further includes a duty cycle for the uLED550 corresponding to the uLED ID. The memory 1662 can further includeV_(MIN) 884, V_(MAX) 880, and a frequency of V_(LED) 106. The memory1662 can further include a reference time that can be used by thecontroller 1660 to determine when V_(LED) 106 will be at V_(f) 882 ofthe uLED 550. The controller 1660 can thus determine, based on the datain the memory 1662, when to send commands to the driver 444 to operatethe uLED 550 such that V_(LED)>V_(f) for as much of the uLED 550 dutycycle as possible.

Embodiments that modulate V_(LED) 106 can recover an efficiency of thedriver 444 to well-above 80% with just a few hundred mV modulation rangein cases of typical dispersions values around 100 mV. A total peakcurrent drawn by the voltage supply 102 can only moderately increase asa function of the modulation amplitude set by the proposed controlscheme. Therefore, interconnected related RMS losses are not expected tosignificantly worsen.

FIG. 17 illustrates, by way of example, a diagram of an embodiment of amethod 1700 for driving a uLED matrix die. The method 1700 can beperformed, at least in part, by the voltage supply 102, the matrix ofuLEDs 104, the controller 1660, driver 444, other component, or acombination thereof. The method 1700, as illustrated, includesproviding, by a power supply, an alternating current voltage (V_(LED))with a minimum voltage (V_(MIN)) and a maximum voltage (V_(MAX)),V_(MIN) being sufficient to drive a plurality of micro light emittingdiodes (uLEDs) of a uLED die using a plurality of uLED drivers, atoperation 1702; identifying, by a controller coupled to the uLEDdrivers, a uLED of the plurality of uLEDs with a forward voltage (V_(f))greater than V_(MIN), at operation 1704; and altering, by thecontroller, a time of a rising edge of a pulse width modulation (PWM)-ontime of the uLED such that V_(f) of the uLED is less than V_(LED) forthe PWM-on time, at operation 1706.

The method 1700 can further include further identifying, by thecontroller, that the PWM on time of the uLED overlaps with a time atwhich the V_(LED) is less than V_(f) before altering the time of therising edge. The method 1700 can further include identifying, by thecontroller, that an amount of time V_(f) is less than V_(LED) is lessthan the PWM on time. The method 1700 can further include reducing thePWM on time and increasing a peak current of a pixel driver at the uLEDdriver of the uLED. The method 1700 can further include causing, by thecontroller, V_(MAX) and V_(MIN) to increase in magnitude whilemaintaining a same frequency.

The method 1700 can further include identifying that the PWM on time ofthe uLED overlaps with a time at which the V_(LED) is less than V_(f)includes determining respective times corresponding to rising edge andfalling edges of the PWM on time based on a duty cycle of the uLED. Themethod 1700 can further include, wherein identifying the time PWM ontime of the uLED overlaps with a time at which the V_(LED) is less thanV_(f) includes using a frequency and a reference time indicating a timeat which V_(LED) equals V_(MAX) or V_(MIN) to identify one of the timeof the rising edge or the falling edge overlaps with the time at whichthe V_(LED) is less than V_(f). The method 1700 can further include,wherein a drive current of the uLED of the uLED die with V_(f) greaterthan V_(MIN) is modified such that an average drive current of the uLEDis driven to a target average power.

What follows are some details regarding the matrix of uLEDs 104 and someapplication considerations followed by some examples.

FIG. 18 illustrates in more detail an embodiment of a chip-levelimplementation of a system 1800 supporting functionality, such asdiscussed with respect to, for example, FIGS. 6-17. The system 1800includes a command and control module 1816 (sometimes called thecontroller, which may be similar to or the same as the controller 1660of FIG. 16) able to implement pixel or group pixel level control ofamplitude and duty cycle for circuitry and procedures such as discussedwith respect to FIGS. 6-17 and elsewhere herein. In some embodiments,the system 1800 further includes a frame buffer 1810 for holdinggenerated or processed images that can be supplied to the matrix ofuLEDs 1820. Other modules can include digital control interfaces, suchas (e.g., an Inter-Integrated Circuit (I²C) serial bus) or SerialPeripheral Interface (SPI) (1814), that are configured to transmitcontrol data or instructions or response data.

In operation, system 1800 can accept image or other data from a vehicleor other source that arrives via the SPI interface 1814. Successiveimages or video data can be stored in an image frame buffer 1810. If noimage data is available, one or more standby images held in a standbyimage buffer 1811 can be directed to the image frame buffer 1810. Suchstandby images can include, for example, an intensity and spatialpattern consistent with legally allowed low beam headlamp radiationpatterns of a vehicle, or default light radiation patterns forarchitectural lighting or displays.

In operation, pixels in the images are used to define response ofcorresponding LED pixels in the active, with intensity and spatialmodulation of LED pixels being based on the image(s). To reduce datarate issues, groups of pixels (e.g., 5×5 blocks) can be controlled assingle blocks in some embodiments. In some embodiments, high speed andhigh data rate operation is supported, with pixel values from successiveimages able to be loaded as successive frames in an image sequence at arate between 30 Hz and 100 Hz, with 60 Hz being typical. PWM can be usedto control each pixel to emit light in a pattern and with an intensityat least partially dependent on the image held in the image frame buffer1810.

In some embodiments, the system 1800 can receive logic power via V_(dd)and V_(ss) pins. An active matrix receives power for LED array controlby multiple V_(LED) and V_(Cathode) pins. The SPI 1814 can provide fullduplex mode communication using a master-slave architecture with asingle master. The master device originates the frame for reading andwriting. Multiple slave devices are supported through selection withindividual slave select (SS) lines. Input pins can include a MasterOutput Slave Input (MOSI), a Master Input Slave Output (MISO), a chipselect (SC), and clock (CLK), all connected to the SPI interface 1814.The SPI interface 1814 connects to an address generator, frame buffer,and a standby frame buffer. Pixels can have parameters set and signalsor power modified (e.g. by power gating before input to the framebuffer, or after output from the frame buffer via pulse width modulationor power gating) by a command and control module. The SPI interface 1814can be connected to an address generation module 1818 that in turnprovides row and address information to the active matrix 1820. Theaddress generation module 1818 in turn can provide the frame bufferaddress to the frame buffer 1810.

In some embodiments, the command and control module 1816 can beexternally controlled via the serial bus 1812. A clock (SCL) pin anddata (SDA) pin, such as with 7-bit addressing can be supported. Thecommand and control module 1816 can include a digital to analogconverter (DAC) and two analog to digital converters (ADC). The DAC andADC are respectively used to set V_(bias) for a connected active matrix,help determine maximum V_(f), and determine system temperature. Alsoconnected are an oscillator (OSC) to set the pulse width modulationoscillation (PWMOSC) frequency for the active matrix 1820. In oneembodiment, a bypass line is also present to allow address of individualpixels or pixel blocks in the active matrix for diagnostic, calibration,or testing purposes. The active matrix 1820 can be further supported byrow and column select that is used to address individual pixels, whichare supplied with a data line, a bypass line, a PWMOSC line, a V_(bias)line, and a V_(f) line.

As will be understood by a person of ordinary skill in the art, in someembodiments the described circuitry and active matrix 1820 (similar toor same as the matrix of uLEDs 104) can be packaged and optionallyinclude a submount or printed circuit board connected for powering andcontrolling light production by the semiconductor LED. In certainembodiments, the printed circuit board can also include electrical vias,heat sinks, ground planes, electrical traces, and flip chip or othermounting systems. The submount or printed circuit board may be formed ofany suitable material, such as ceramic, silicon, aluminum, etc. If thesubmount material is conductive, an insulating layer is formed over thesubstrate material, and the metal electrode pattern is formed over theinsulating layer. The submount can act as a mechanical support,providing an electrical interface between electrodes on the LED and apower supply, and also provide heat sinking.

In some embodiments, the active matrix 1820 can be formed from lightemitting elements of various types, sizes, and layouts. In oneembodiment, one or two dimensional matrix arrays of individuallyaddressable light emitting diodes (LEDs) can be used. Commonly N×Marrays where N and M are respectively between two and one thousand canbe used. Individual LED structures can have a square, rectangular,hexagonal, polygonal, circular, arcuate or other surface shape. Arraysof the LED assemblies or structures can be arranged in geometricallystraight rows and columns, staggered rows or columns, curving lines, orsemi-random or random layouts. LED assemblies can include multiple LEDsformed as individually addressable pixel arrays are also supported. Insome embodiments, radial or other non-rectangular grid arrangements ofconductive lines to the LED can be used. In other embodiments, curving,winding, serpentine, and/or other suitable non-linear arrangements ofelectrically conductive lines to the LEDs can be used.

In some embodiments, arrays of microLEDs (μLEDs or uLEDs) can be used.uLEDs can support high density pixels having a lateral dimension lessthan 100 μm by 100 μm. In some embodiments, uLEDs with dimensions ofabout 50 μm in diameter or width and smaller can be used. Such uLEDS canbe used for the manufacture of color displays by aligning, in closeproximity, uLEDs comprising red, blue, and green wavelengths. In otherembodiments, uLEDS can be defined on a monolithic gallium nitride (GaN)or other semiconductor substrate, formed on segmented, partially, orfully divided semiconductor substrate, or individually formed or panelassembled as groupings of uLEDs. In some embodiments, the active matrix1120 can include small numbers of uLEDs positioned on substrates thatare centimeter scale area or greater. In some embodiments, the activematrix 1120 can support uLED pixel arrays with hundreds, thousands, ormillions of LEDs positioned together on centimeter scale area substratesor smaller. In some embodiments, uLEDS can include LEDs sized between 30microns and 500 microns. In some embodiments, each of the light emittingpixels in the light emitting pixel array can be positioned at least 1millimeter apart to form a sparse LED array. In other embodiments sparseLED arrays of light emitting pixels can be positioned less than 1millimeter apart and can be spaced apart by distances ranging from 30microns to 500 microns. The LEDs can be embedded in a solid or aflexible substrate, which can be at least in part transparent. Forexample, the light emitting pixel arrays can be at least partiallyembedded in glass, ceramic, or polymeric materials.

Light emitting matrix pixel arrays, such as discussed herein, maysupport applications that benefit from fine-grained intensity, spatial,and temporal control of light distribution. This may include, but is notlimited to, precise spatial patterning of emitted light from pixelblocks or individual pixels. Depending on the application, emitted lightmay be spectrally distinct, adaptive over time, and/or environmentallyresponsive. The light emitting pixel arrays may provide pre-programmedlight distribution in various intensity, spatial, or temporal patterns.The emitted light may be based at least in part on received sensor dataand may be used for optical wireless communications. Associated opticsmay be distinct at a pixel, pixel block, or device level. An examplelight emitting pixel array may include a device having a commonlycontrolled central block of high intensity pixels with an associatedcommon optic, whereas edge pixels may have individual optics. Commonapplications supported by light emitting pixel arrays include videolighting, automotive headlights, architectural and area illumination,street lighting, and informational displays.

Light emitting matrix pixel arrays may be used to selectively andadaptively illuminate buildings or areas for improved visual display orto reduce lighting costs. In addition, light emitting pixel arrays maybe used to project media facades for decorative motion or video effects.In conjunction with tracking sensors and/or cameras, selectiveillumination of areas around pedestrians may be possible. Spectrallydistinct pixels may be used to adjust the color temperature of lighting,as well as support wavelength specific horticultural illumination.

Street lighting is an application that may benefit from use of lightemitting pixel arrays. A single light emitting array may be used tomimic various street light types, allowing, for example, switchingbetween a Type I linear streetlight and a Type IV semicircularstreetlight by appropriate activation or deactivation of selectedpixels. In addition, street lighting costs may be lowered by adjustinglight beam intensity or distribution according to environmentalconditions or time of use. For example, light intensity and area ofdistribution may be reduced when pedestrians are not present. If pixelsof the light emitting pixel array are spectrally distinct, the colortemperature of the light may be adjusted according to respectivedaylight, twilight, or night conditions.

Light emitting arrays are also suited for supporting applicationsrequiring direct or projected displays. For example, warning, emergency,or informational signs may all be displayed or projected using lightemitting arrays. This allows, for example, color changing or flashingexit signs to be projected. If a light emitting array is composed of alarge number of pixels, textual or numerical information may bepresented. Directional arrows or similar indicators may also beprovided.

Vehicle headlamps are a light emitting array application that requireslarge pixel numbers and a high data refresh rate. Automotive headlightsthat actively illuminate only selected sections of a roadway can used toreduce problems associated with glare or dazzling of oncoming drivers.Using infrared cameras as sensors, light emitting pixel arrays activateonly those pixels needed to illuminate the roadway, while deactivatingpixels that may dazzle pedestrians or drivers of oncoming vehicles. Inaddition, off-road pedestrians, animals, or signs may be selectivelyilluminated to improve driver environmental awareness. If pixels of thelight emitting pixel array are spectrally distinct, the colortemperature of the light may be adjusted according to respectivedaylight, twilight, or night conditions. Some pixels may be used foroptical wireless vehicle to vehicle communication.

An LED light module can include matrix LEDS, alone or in conjunctionwith primary or secondary optics, including lenses or reflectors. Toreduce overall data management requirements, the light module can belimited to on/off functionality or switching between relatively fewlight intensity levels. Full pixel level control of light intensity isnot necessarily supported.

In operation, pixels in the images are used to define response ofcorresponding LED pixels in the pixel module, with intensity and spatialmodulation of LED pixels being based on the image(s). To reduce datarate issues, groups of pixels (e.g. 5×5 blocks) can be controlled assingle blocks in some embodiments. High speed and high data rateoperation is supported, with pixel values from successive images able tobe loaded as successive frames in an image sequence at a rate between 30Hz and 100 Hz, with 60 Hz being typical. In conjunction with a pulsewidth modulation module, each pixel in the pixel module can be operatedto emit light in a pattern and with intensity at least partiallydependent on the image held in the image frame buffer.

In the foregoing described embodiments, intensity of a uLED can beseparately controlled and adjusted by setting appropriate ramp times andpulse width for each LED pixel using a suitable lighting logic, controlmodule, and/or PWM module. Outlier pixel voltage management can provideLED pixel activation to provide reliable patterned lighting. A controlsystem 1900 that can provide voltage supply 102 voltage management isillustrated in FIG. 19. As seen in FIG. 19, a matrix micro-LED array1920 (similar to or same as the matrix of uLEDs 104) can contain one ormore arrays of thousands to millions of microscopic LED pixels thatactively emit light and are individually controlled. To emit light in apattern or sequence that results in display of an image, the currentlevels of the micro-LED pixels at different locations on an array areadjusted individually according to a specific image. This can involve aPWM, which turns on and off the pixels at a certain frequency. DuringPWM operation, the average DC current through a pixel is the product ofthe electrical current amplitude and the PWM duty cycle, which is theratio between the conduction time and the period or cycle time.

FIG. 19 illustrates, by way of example, a logical block diagram of asystem 1900 that includes circuitry that can be included in a uLEDpackage. Processing modules that facilitate efficient usage of thesystem 1900 are illustrated in FIG. 19. The system 1900 includes acontrol module 1916 (similar to or same as the control module 1816) ableto implement pixel or group pixel level control of amplitude and dutycycle for circuitry and procedures such as discussed with respect toFIGS. 6-18. In some embodiments, the system 1900 further includes animage processing module 1904 to generate, process, or transmit an image,and digital control interfaces 1913, such as inter-integrated circuit(I²C), serial peripheral interface (SPI), controller area network (CAN),universal asynchronous receiver transmitter (UART), or the like, that isconfigured to transmit control data and/or instructions. The digitalcontrol interfaces 1913 and control module 1916 may include a systemmicrocontroller and any type of wired or wireless module configured toreceive a control input from an external device. By way of example, awireless module may include Bluetooth®, Zigbee, Z-wave, mesh, WiFi, nearfield communication (NFC) and/or peer to peer modules may be used. Themicrocontroller may be any type of special purpose computer or processorthat may be embedded in an LED lighting system and configured orconfigurable to receive inputs from the wired or wireless module orother modules in the LED system and provide control signals to othermodules based thereon. Algorithms implemented by the microcontroller orother suitable control module 1816 may be implemented in a computerprogram, software, or firmware incorporated in a non-transitorycomputer-readable storage medium for execution by the special purposeprocessor. Examples of non-transitory computer-readable storage mediumsinclude a read only memory (ROM), a random access memory (RAM), aregister, cache memory, and semiconductor memory devices. The memory maybe included as part of the microcontroller or may be implementedelsewhere, either on or off a printed circuit or electronics board.Non-transitory does not mean incapable of motion (incapable of being intransit).

The term module, as used herein, may refer to electrical and/orelectronic components disposed on individual circuit boards that may besoldered to one or more electronics boards. The term module may,however, also refer to electrical and/or electronic components thatprovide similar functionality, but which may be individually soldered toone or more circuit boards in a same region or in different regions.

The control module 1916 can further include the image processing module1904 and the digital control interfaces 1913, such as I²C. As will beappreciated, in some embodiments an image processing computation may bedone by the control module 1916 through directly generating a modulatedimage. Alternatively, a standard image file can be processed orotherwise converted to provide modulation to match the image. Image datathat mainly contains PWM duty cycle values can be processed for allpixels in image processing module 1904. Since amplitude is a fixed valueor rarely changed value, amplitude related commands can be givenseparately through a simpler digital interface, such as I²C. The controlmodule 1916 interprets digital data, which can be used by PWM generator1910 to generate PWM signals for pixels, and by Digital-to-AnalogConverter (DAC) block 1912 to generate the control signals for obtainingthe required current source amplitude.

In some embodiments, the active matrix 1920 in FIG. 19 can include mpixels including m common anode LEDs. In one example embodiment thepixel unit includes a single LED, LED1, and three transconductancedevices (e.g., MOSFET) switches M1 through M3, and is supplied by thevoltage supply V1 (sometimes called V_(LED)). M3 is an N-channel metaloxide semiconductor field effect transistor (MOSFET) whose gate iscoupled to the amplitude control signal to generate the required currentsource amplitude. The P-channel MOSFET M1 is in parallel to LED1 andforms a totem pole pair with the N-channel MOSFET M2. The gates of theM1 and M2 transistor pair are tied together and coupled to the PWMsignal. Therefore, when PWM is high, M1 will be turned off and M2 willbe turned on. A current will flow through LED1, M2, and M3 with a valuedetermined by the amplitude control signal coupled to M3 gate. When PWMis low, M1 will be turned on and M2 will be turned off. Consequently,the current source of M3 will be cut off and the LED will be fastdischarged through M1.

FIG. 20 illustrates, by way of example, a block diagram of an embodimentof a machine 2000 (e.g., a computer system) to implement one or moreembodiments. The machine 2000 can implement a technique for managingunderdriven or undriven uLEDs of a uLED die. The controller 1660,voltage supply 102, or a component thereof can include one or more ofthe components of the machine 2000. One or more of the controller 1660,voltage supply 102, or a component thereof can be implemented, at leastin part, using a component of the machine 2000. One example machine 2000(in the form of a computer), may include a processing unit 2002, memory2003, removable storage 2010, and non-removable storage 2012. Althoughthe example computing device is illustrated and described as machine2000, the computing device may be in different forms in differentembodiments. For example, the computing device may instead be asmartphone, a tablet, smartwatch, or other computing device includingthe same or similar elements as illustrated and described regarding FIG.20. Devices such as smartphones, tablets, and smartwatches are generallycollectively referred to as mobile devices. Further, although thevarious data storage elements are illustrated as part of the machine2000, the storage may also or alternatively include cloud-based storageaccessible via a network, such as the Internet.

Memory 2003 may include volatile memory 2014 and non-volatile memory2008. The machine 2000 may include—or have access to a computingenvironment that includes—a variety of computer-readable media, such asvolatile memory 2014 and non-volatile memory 2008, removable storage2010 and non-removable storage 2012. Computer storage includes randomaccess memory (RAM), read only memory (ROM), erasable programmableread-only memory (EPROM) & electrically erasable programmable read-onlymemory (EEPROM), flash memory or other memory technologies, compact discread-only memory (CD ROM), Digital Versatile Disks (DVD) or otheroptical disk storage, magnetic cassettes, magnetic tape, magnetic diskstorage or other magnetic storage devices capable of storingcomputer-readable instructions for execution to perform functionsdescribed herein.

The machine 2000 may include or have access to a computing environmentthat includes input 2006, output 2004, and a communication connection2016. Output 2004 may include a display device, such as a touchscreen,that also may serve as an input device. The input 2006 may include oneor more of a touchscreen, touchpad, mouse, keyboard, camera, one or moredevice-specific buttons, one or more sensors integrated within orcoupled via wired or wireless data connections to the machine 2000, andother input devices. The computer may operate in a networked environmentusing a communication connection to connect to one or more remotecomputers, such as database servers, including cloud-based servers andstorage. The remote computer may include a personal computer (PC),server, router, network PC, a peer device or other common network node,or the like. The communication connection may include a Local AreaNetwork (LAN), a Wide Area Network (WAN), cellular, Institute ofElectrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi), Bluetooth,or other networks.

Computer-readable instructions stored on a computer-readable storagedevice are executable by the processing unit 2002 (sometimes calledprocessing circuitry) of the machine 2000. A hard drive, CD-ROM, and RAMare some examples of articles including a non-transitorycomputer-readable medium such as a storage device. For example, acomputer program 2018 may be used to cause processing unit 2002 toperform one or more methods or algorithms described herein.

To further illustrate the apparatus and related method disclosed herein,a non-limiting list of examples is provided below. Each of the followingnon-limiting examples can stand on its own or can be combined in anypermutation or combination with any one or more of the other examples.

In Example 1 a method includes providing, by a power supply, analternating current voltage (V_(LED)) with a minimum voltage (V_(MIN))and a maximum voltage (V_(MAX)), V_(MIN) being sufficient to drive aplurality of micro light emitting diodes (uLEDs) of a uLED die using aplurality of uLED drivers, identifying, by a controller coupled to theuLED drivers, a uLED of the plurality of uLEDs with a forward voltage(V_(f)) greater than V_(MIN), and altering, by the controller, a time ofa rising edge of a pulse width modulation (PWM)-on time of the uLED suchthat V_(f) of the uLED is less than V_(LED) for the PWM-on time.

In Example 2, Example 1 can further include further identifying, by thecontroller, that the PWM on time of the uLED overlaps with a time atwhich the V_(LED) is less than V_(f) before altering the time of therising edge.

In Example 3, at least one of Examples 1-2 can further includeidentifying, by the controller, that an amount of time V_(f) is lessthan V_(LED) is less than the PWM on time.

In Example 4, Example 3 can further include reducing the PWM on time andincreasing a peak current of a pixel driver at the uLED driver of theuLED.

In Example 5, at least one of Examples 3-4 can further include causing,by the controller, V_(MAX) and V_(MIN) to increase in magnitude whilemaintaining a same frequency.

In Example 6, at least one of Examples 1-5 can further include, whereinidentifying that the PWM on time of the uLED overlaps with a time atwhich the V_(LED) is less than V_(f) includes determining respectivetimes corresponding to rising edge and falling edges of the PWM on timebased on a duty cycle of the uLED.

In Example 7, Example 6 can further include, wherein identifying thetime PWM on time of the uLED overlaps with a time at which the V_(LED)is less than V_(f) includes using a frequency and a reference timeindicating a time at which V_(LED) equals V_(MAX) or V_(MIN) to identifyone of the time of the rising edge or the falling edge overlaps with thetime at which the V_(LED) is less than V_(f).

In Example 8, at least one of Examples 1-7 can further include, whereina drive current of the uLED of the uLED die with V_(f) greater thanV_(MIN) is modified such that an average drive current of the uLED isdriven to a target average power.

Example 9 includes a system comprising a power supply configured toprovide an alternating current voltage (V_(LED)) with a minimum voltage(V_(MIN)) and a maximum voltage (V_(MAX)), V_(MIN) sufficient to drive amajority of micro light emitting diodes (uLEDs) of a uLED die using uLEDdrivers of the uLED die, and a controller coupled to the uLED drivers,the controller configured to identify a uLED of the uLEDs with a forwardvoltage (V_(f)) greater than V_(MIN) and alter a time of a rising edgeof a pulse width modulation (PWM) on time of the uLED such that V_(f) ofthe uLED is less than V_(LED) for the PWM on time.

In Example 10, Example 9 can further include, wherein the controller isfurther configured to identify that the PWM on time of the uLED overlapswith a time at which the V_(LED) is less than V_(f) before altering thetime of the rising edge.

In Example 11, at least one of Examples 9-10 can further include,wherein the controller is further configured to identify that an amountof time V_(f) is less than V_(LED) is less than the PWM on time.

In Example 12, Example 11 can further include, wherein the controller isfurther configured to reduce the PWM on time and increasing a peakcurrent of a pixel driver at the uLED driver of the uLED.

In Example 13, at least one of Examples 11-12 can further include,wherein the controller is further configured to cause V_(MAX) andV_(MIN) to increase in magnitude while maintaining a same frequency.

In Example 14, at least one of Examples 9-13 can further include,wherein identifying that the PWM on time of the uLED overlaps with atime at which the V_(LED) is less than V_(f) includes determiningrespective times corresponding to rising edge and falling edges of thePWM on time based on a duty cycle of the uLED.

In Example 15, Example 14 can further include, wherein identifying thetime PWM on time of the uLED overlaps with a time at which the V_(LED)is less than V_(f) includes using a frequency and a reference timeindicating a time at which V_(LED) equals V_(MAX) or V_(MIN) to identifyone of the time of the rising edge or the falling edge overlaps with thetime at which the V_(LED) is less than V_(f).

Example 16 includes a machine-readable medium including instructionsthat, when executed by a machine, cause the machine to performoperations comprising providing an alternating current voltage (V_(LED))with a minimum voltage (V_(MIN)) and a maximum voltage (V_(MAX)),V_(MIN) sufficient to drive a majority of micro light emitting diodes(uLEDs) of a uLED die using uLED drivers of the uLED die, identifying auLED of the uLEDs with a forward voltage (V_(f)) greater than V_(MIN),and altering a time of a rising edge of a pulse width modulation (PWM)on time of the uLED such that V_(f) of the uLED is less than V_(LED) forthe PWM on time.

In Example 17, Example 16 can further include, wherein the operationsfurther comprise further identifying that the PWM on time of the uLEDoverlaps with a time at which the V_(LED) is less than V_(f) beforealtering the time of the rising edge.

In Example 18, at least one of Examples 16-17 can further includewherein the operations further comprise identifying that an amount oftime V_(f) is less than V_(LED) is less than the PWM on time.

In Example 19, Example 18 can further include, wherein the operationsfurther comprise reducing the PWM on time and increasing a peak currentof a pixel driver at the uLED driver of the uLED.

In Example 20, at least one of Examples 18-19 can further include,wherein the operations further comprise causing V_(MAX) and V_(MIN) toincrease in magnitude while maintaining a same frequency.

While example embodiments of the present disclosed subject matter havebeen shown and described herein, it will be obvious to those skilled inthe art that such embodiments are provided by way of example only.Numerous variations, changes, and substitutions will now occur to thoseskilled in the art, upon reading and understanding the material providedherein, without departing from the disclosed subject matter. It shouldbe understood that various alternatives to the embodiments of thedisclosed subject matter described herein may be employed in practicingthe various embodiments of the subject matter. It is intended that thefollowing claims define the scope of the disclosed subject matter andthat methods and structures within the scope of these claims and theirequivalents be covered thereby.

What is claimed is:
 1. A method comprising: providing, by a powersupply, an alternating current voltage (V_(LED)) with a minimum voltage(V_(MIN)) and a maximum voltage (V_(MAX)), V_(MIN) being sufficient todrive a plurality of micro light emitting diodes (uLEDs) of a uLED dieusing a plurality of uLED drivers; identifying, by a controller coupledto the uLED drivers, a uLED of the plurality of uLEDs with a forwardvoltage (V_(f)) greater than V_(MIN); and altering, by the controller, atime of a rising edge of a pulse width modulation (PWM)-on time of theuLED such that V_(f) of the uLED is less than V_(LED) for the PWM-ontime.
 2. The method of claim 1, further comprising further identifying,by the controller, that the PWM on time of the uLED overlaps with a timeat which the V_(LED) is less than V_(f) before altering the time of therising edge.
 3. The method of claim 1, further comprising identifying,by the controller, that an amount of time V_(f) is less than V_(LED) isless than the PWM on time.
 4. The method of claim 3, further comprising,reducing the PWM on time and increasing a peak current of a pixel driverat the uLED driver of the uLED.
 5. The method of claim 3, furthercomprising causing, by the controller, V_(MAX) and V_(MIN) to increasein magnitude while maintaining a same frequency.
 6. The method of claim1, wherein identifying that the PWM on time of the uLED overlaps with atime at which the V_(LED) is less than V_(f) includes determiningrespective times corresponding to rising edge and falling edges of thePWM on time based on a duty cycle of the uLED.
 7. The method of claim 6,wherein identifying the time PWM on time of the uLED overlaps with atime at which the V_(LED) is less than V_(f) includes using a frequencyand a reference time indicating a time at which V_(LED) equals V_(MAX)or V_(MIN) to identify one of the time of the rising edge or the fallingedge overlaps with the time at which the V_(LED) is less than V_(f). 8.The method of claim 1, wherein a drive current of the uLED of the uLEDdie with V_(f) greater than V_(MIN) is modified such that an averagedrive current of the uLED is driven to a target average power.
 9. Asystem comprising: a power supply configured to provide an alternatingcurrent voltage (V_(LED)) with a minimum voltage (V_(MIN)) and a maximumvoltage (V_(MAX)), V_(MIN) sufficient to drive a majority of micro lightemitting diodes (uLEDs) of a uLED die using uLED drivers of the uLEDdie; and a controller coupled to the uLED drivers, the controllerconfigured to: identify a uLED of the uLEDs with a forward voltage(V_(f)) greater than V_(MIN) and alter a time of a rising edge of apulse width modulation (PWM) on time of the uLED such that V_(f) of theuLED is less than V_(LED) for the PWM on time.
 10. The system of claim9, wherein the controller is further configured to identify that the PWMon time of the uLED overlaps with a time at which the V_(LED) is lessthan V_(f) before altering the time of the rising edge.
 11. The systemof claim 9, wherein the controller is further configured to identifythat an amount of time V_(f) is less than V_(LED) is less than the PWMon time.
 12. The system of claim 11, wherein the controller is furtherconfigured to reduce the PWM on time and increasing a peak current of apixel driver at the uLED driver of the uLED.
 13. The system of claim 11,wherein the controller is further configured to cause V_(MAX) andV_(MIN) to increase in magnitude while maintaining a same frequency. 14.The system of claim 9, wherein identifying that the PWM on time of theuLED overlaps with a time at which the V_(LED) is less than V_(f)includes determining respective times corresponding to rising edge andfalling edges of the PWM on time based on a duty cycle of the uLED. 15.The system of claim 14, wherein identifying the time PWM on time of theuLED overlaps with a time at which the V_(LED) is less than V_(f)includes using a frequency and a reference time indicating a time atwhich V_(LED) equals V_(MAX) or V_(MIN) to identify one of the time ofthe rising edge or the falling edge overlaps with the time at which theV_(LED) is less than V_(f).
 16. A machine-readable medium includinginstructions that, when executed by a machine, cause the machine toperform operations comprising: providing an alternating current voltage(V_(LED)) with a minimum voltage (V_(MIN)) and a maximum voltage(V_(MAX)), V_(MIN) sufficient to drive a majority of micro lightemitting diodes (uLEDs) of a uLED die using uLED drivers of the uLEDdie; identifying a uLED of the uLEDs with a forward voltage (V_(f))greater than V_(MIN); and altering a time of a rising edge of a pulsewidth modulation (PWM) on time of the uLED such that V_(f) of the uLEDis less than V_(LED) for the PWM on time.
 17. The machine-readablemedium of claim 16, wherein the operations further comprise furtheridentifying that the PWM on time of the uLED overlaps with a time atwhich the V_(LED) is less than V_(f) before altering the time of therising edge.
 18. The machine-readable medium of claim 16, wherein theoperations further comprise identifying that an amount of time V_(f) isless than V_(LED) is less than the PWM on time.
 19. The machine-readablemedium of claim 18, wherein the operations further comprise reducing thePWM on time and increasing a peak current of a pixel driver at the uLEDdriver of the uLED.
 20. The machine-readable medium of claim 18, whereinthe operations further comprise causing V_(MAX) and V_(MIN) to increasein magnitude while maintaining a same frequency.